This invention relates to manually operable signal generating devices of a type suitable for use as interface devices for generating control signals which can be used to control movement of at least one discrete image portion in a display which is produced on the screen of a display device, for instance a television monitor.
Known signal generating devices of the above type are the roller- or tracker-ball and the toggle or joy stick. Each of these known devices can generate control signals for controlling movement of a discrete image portion such that the latter can be positioned anywhere in the display by appropriate manual manipulation of the device. The control signals generated by the devices can be considered to be co-ordinate control signals which represent the co-ordinates of any selected position in the display and which are used to drive display circuits to control the movement of the image portion from its current position in the display to the selected position.
In a computer-based information display system, there are many instances where interactive operation of the system by a user is based on visual feedback from displayed information. It is well-established that the above-mentioned known signal generating devices can be employed as interface devices to effect such interactive operation, and that the visual feedback from the display to a user obviates the need for the user having to look at such an interface device while operating it.
However, with each of these known signal generating devices the entire hand rather than a single finger has to be used to operate them, which can be a disadvantage when the device forms part of a user control console containing other types of interface device, for instance a keyboard. In particular, the need to engage the device with the entire hand can restrict the speed at which it can be taken into use. Also, a tracker- or roller-ball is intrinsically large in three dimensions, so that mounting it in a control console can be a problem; while problems of mechanical instability and inaccuracy can arise with a toggle or joy-stick.